DHHS (NIOSH) Publication No. 2012-139, Loss of Start-Up Oxygen in CSE SR-100 Self-Contained Self-Rescuers 2012-139[1]

8/2/2019 DHHS (NIOSH) Publication No. 2012-139, Loss of Start-Up Oxygen in CSE SR-100 Self-Contained Self-Rescuers 2012-139[1]

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Loss of Start-Up Oxygen inCSE SR-100 Self-ContainedSelf-Rescuers

of Health and Human Services


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Loss of Start-Up Oxygen in CSE SR-100 Self-ContainedSelf-Rescuers

Robert Stein, Heinz Ahlers, Roland Berry Ann

DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention

National Institute for Occupational Safety and HealthApril 2012


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This document is in the public domain and may be freelycopied or reprinted.

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For a monthly update on news at NIOSH, subscribe to NIOSH eNews by visiting

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DHHS (NIOSH) Publication No. 2012139

April 2012

SAFER HEALTHIER PEOPLE

ii
mailto:[email protected]://www.cdc.gov/nioshhttp://www.cdc.gov/niosh/eNewsmailto:[email protected]://www.cdc.gov/nioshhttp://www.cdc.gov/niosh/eNews


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Loss of Start-Up Oxygen in CSE SR-100 Self-Contained Self-Rescuers

Robert Stein, Heinz Ahlers, Roland Berry Ann

Executive Summary

This report describes a National Institute for Occupational Safety and Health (NIOSH) and Mine

Safety and Health Administration (MSHA) investigation assessing the prevalence of a lack ofsufficient start-up oxygen in CSE SR-100 self-contained self-rescuer (SCSR) devices.

The availability of sufficient start-up oxygen is critical to the performance of the SR-100. As

part of a routine field testing program of SCSRs used in coal mines, NIOSH and MSHA detected

two SR-100s that lacked sufficient start-up oxygen. CSE Corporation subsequently discovered

one SCSR that lacked sufficient start-up oxygen in that companys internal quality controlprogram and voluntarily stopped further production and sales of SR-100s.

NIOSH developed a protocol to test for the presence of start-up oxygen in field-deployed SR-

100s. The purpose of the test was to determine if the failure rate of the start-up oxygen in the

population of 70,000 field-deployed units exceeded 1%. NIOSH and MSHA used American

Society for Quality (ASQ), Sampling Procedures and Tables for Inspection of Isolated Lots byAttributes (ASQC Q3-1988)

1. In assessing the SR-100s, if no more than 3 failures of start-up

oxygen occurred in the 500-unit random sample, the SR-100 could be accepted as meeting the

Limiting Quality (LQ) rate of 1.25% for start-up oxygen performance.

NIOSH tested five hundred field-deployed devices collected from coal mines throughout theUnited States. NIOSH observed 5 start-up oxygen failures in the 500 units it tested. Themaximum number of failures allowed under the LQ rate of 1.25% was exceeded; therefore, the

1% maximum allowable failure rate under the protocol was not met.

1 American National Standard, Sampling Procedures and Tables for Inspection of Isolated Lots by Attributes,(ANSI/ASQC Standard Q3-1988), American Society for Quality, 1988.

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Contents

Executive Summary ........................................................................................................iiiContents ..........................................................................................................................ivAcronyms and Abbreviations ...........................................................................................viIntroduction ..................................................................................................................... 1Methods .......................................................................................................................... 2Results ............................................................................................................................ 4Major Findings ................................................................................................................. 9Appendix 1 .................................................................................................................... 10

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Figures

Figure 1. Age histogram of SR-100 population ....................................................................... 5Figure 2. Age histogram of targeted sample............................................................................ 5Figure 3. Age histogram of tested sample ............................................................................... 6

Figure 4. Unit 154821 ...................................................................................................... 8Figure 5. Unit 154821 Dented bottom cover. ....................................................................... 8Figure 6. Unit 249530 .................................................................................................................. 8Figure 7. Unit 114752 .................................................................................................................. 8Figure 8. Unit 251475 .................................................................................................................. 9Figure 9. Unit 249607 .................................................................................................................. 9

Tables

Table 1. Inspection Failures ....................................................................................................... 6Table 2. Start-up oxygen failure details .................................................................................... 7

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Acronyms and Abbreviations

ANSI American National Standards InstituteAQL Acceptable Quality Level

ASMD Acoustic Solids Movement DetectorASQ American Society for QualityASQC American Society for Quality ControlCFR Code of Federal RegulationsLQ Limiting QualityLTFE Long-Term Field EvaluationMSHA Mine Safety and Health AdministrationNIOSH National Institute for Occupational Safety and HealthQA Quality AssuranceSCSR Self-Contained Self-RescuerS/N Serial NumberF Degrees Fahrenheit

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Introduction

The National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and

Health Administration (MSHA) jointly approve respirators for use in the nations mines. Under

42 CFR

2

84.3 (Respirators for mine rescue or other emergency use in mines), NIOSH andMSHA must jointly review and issue certificates of approval for respirators used for mine

emergencies and mine rescue, which includes the CSE SR-100, a one-hour SCSR. At the time of

this investigation, the SR-100 was one of three one-hour SCSR models used in the nationsmines.

The SR-100 was approved in 1989 and has since been deployed in underground coal andmetal/nonmetal mines for use in emergency escapes. CSE classified the operation of the start-up

oxygen as a Critical attribute. The regulation (in section 84.41) classifies potential defects as

follows:

(1) Critical. A defect that judgment and experience indicate is likely to result in a

condition immediately hazardous to life or health for individuals using or depending upon

the respirator;(2)Major A. A defect, other than critical, that is likely to result in failure to the degree

that the respirator does not provide any respiratory protection, or a defect that reduces

protection and is not detectable by the user;(3)Major B. A defect, other than Major A or critical, that is likely to result in reduced

respiratory protection, and is detectable by the user; and

(4)Minor. A defect that is not likely to materially reduce the usability of the respirator

for its intended purpose, or a defect that is a departure from established standards and haslittle bearing on the effective use or operation of the respirator.

To ensure the ongoing reliability of approved mine escape respirators, NIOSH and MSHAconduct a field testing program, referred to as the Long-Term Field Evaluation (LTFE), of

SCSRs used in coal mines. Since 1982, the LTFE has identified reliability issues among the

approved respirators stemming either from the environment or manufacturing. NIOSH notifiedCSE in December 2009 that two SR-100s exhibited little or no start-up oxygen during

performance testing in the most recent phase of the LTFE. CSEs ensuing investigation

identified excessive heat as a contributor to loss of start-up oxygen. However, the heat indicators

on the failed units did not indicate prior exposure to excessive heat, suggesting a factor otherthan excessive heat was responsible for the loss of start-up oxygen.

2 CFR. Code of Federal Regulations. Washington, DC: U.S. Government Printing Office, Office of the Federal

Register.

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During the ongoing investigation, CSE reported to NIOSH and MSHA that routine quality-

assurance testing found an oxygen cylinder in a newly assembled SR-100 that contained aninsufficient quantity of start-up oxygen. CSE immediately and voluntarily ceased production

and sales of the SR-100. CSE subsequently reinspected a large quantity of the pre-filled oxygen

cylinders not yet installed in SR-100s. These oxygen cylinders had been previously confirmed to

have oxygen volume sufficient for the start-up function. But upon reinspection, CSE foundbetween 0.5% and 1% of these pre-filled cylinder assemblies failed inspection due to oxygen

volume loss.

CSE engaged an engineering firm to analyze the loss of start-up oxygen. The engineering firm

concluded that the loss of oxygen occurred at a threaded connection between the cylinder body

and the stopper/outlet assembly. When asked to determine the percentage of affected, assembledSR-100s, CSE responded that it was less than 1% overall. CSE could not identify a systemic

cause or otherwise confine the failure within certain lots. Therefore, the failure could exist

among all field-deployed units.

NIOSH developed a peer-reviewed protocol to evaluate a representative sample of field-deployed SR-100 respirators to determine the extent of the non-conformance. NIOSH andMSHA made a determination for coal-mine deployment that the failure of the start-up oxygen

cylinder should be 1% or less in SR-100s deployed in U.S. coal mines. This criterion was based

on MSHAs rules for coal mining requiring that each miner have an immediately available back-up unit.

NIOSH and MSHA collected more than 500 SR-100s from coal mines throughout the country.

NIOSH tested for low start-up oxygen cylinders from 500 units meeting the inspection criteria.The purpose of these tests was to determine if the failure rate of the start-up oxygen exceeded

1% in the population of 70,000 field-deployed units. The remainder of this report describes themethods, results, major findings and the test protocol used for the investigation.

Methods

Sample Size Determination

Information collected and provided by MSHA in its SCSRinventory3

indicated approximately

70,000 SR-100s were field-deployed during the time of this evaluation. A study protocol wasdeveloped that included a sampling strategy and a testing protocol (see Appendix I). The

sampling plan was designed to detect with 95% confidence that the prevalence of cylinders with

low start-up oxygen (i.e., failure rate) was less than 1.25% for a population of 70,000 units. Thesample selection plan was based on American National Standards (ANSI)/American Society of

3 Further information may be found at http://www.msha.gov/forms/ELawsForms/2000-222.htm

2
http://www.msha.gov/forms/ELawsForms/2000-222.htmhttp://www.msha.gov/forms/ELawsForms/2000-222.htm


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Quality (ASQC) Q3-1988, Sampling Procedures and Tables for Inspection of Isolated Lots by

Attributes (Q3-1988), a quality assurance technique of sampling by attributes. The LimitingQuality (LQ) point nearest to and including the 1% criterion was selected from established tables

with a sample size of 500 units. Three or fewer defective units would mean the failure rate for

the population of 70,000 was less than or equal to 1.25% with 95% confidence.

Recoverable Unit Criteria

Each unit was assessed for compliance with manufacturer inspection criteria. The inspected

characteristics assessed were the Acoustic Solids Movement Detector level (ASMD), moisture

indicators, heat indicator, and several specific physical damage characteristics, which are

grouped together and referred to as damage.

The target sample size was set at 500 recoverable units (see Appendix 1). A recoverable unit

was defined as a unit that could be located, would be relinquished by the owner, and passed allmanufacturer inspection criteria for use. Prior experience collecting respirators from mine

service indicated that more than 500 units would need to be collected and assessed to achieve thedesired sample size. To adjust to difficulty encountered in collecting SR-100s, units werecollected and tested in two major phases. However, the testing procedure did not change from

phase 1 to phase 2.

Phase 1 Unit Collection and Testing

Units were randomly selected by serial number from the full list of 70,000 deployed units

consistent with the original protocol (see Appendix 1). Compensation was offered to mineoperators for any collected unit. Compliance with NIOSH/MSHA approval requires that

owners/users of approved respirators abide by all manufacturer recommendations. Units passingall visual inspection and test criteria were considered recoverable and tested according to the test

plan analysis described in the protocol (Appendix 1). Phase 1 collection and testing of SR-100s

occurred over a period of 5 months.

Phase 2 Unit Collection and Testing

MSHA regulations established at 30 CFR 75.1714-4, promulgated under the Mine

Improvement and New Emergency Response Act of 2006, Pub. L. 109-236 (S. 2803), Section 2

(3)(C)(iii)(II), require coal mine operators to maintain specific quantities (multiple units perminer, per each operators approved Emergency Response Plan) of SCSRs to support mine

escape. Operators were concerned that providing units for testing would result in noncompliance

with MSHA requirements for SCSR coverage before replacement units became available, and

were thus unwilling to provide units for NIOSH testing. As such, it was not possible to completethe collection and testing of SR-100s within a reasonable period of time, using a pure random

collection method.

NIOSH subsequently met with the original protocol peer reviewers to discuss the collection

challenges and determine an alternate strategy. The reviewers agreed that little if any bias would

be introduced if availability was the priority for collecting the remaining units. Availability, as

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used here, indicates the units could be located and their owners were able to part with them

through the NIOSH replacement offers. This protocol change allowed NIOSH to collectrecoverable units from coal mine operators who were able to part with their units and still meet

MSHA backup unit requirements.

NIOSH and MSHA identified two large mine operators who were in the process of withdrawingSR-100s on a mine-by-mine basis. Units were selected by obtaining the highest ranking serial

numbered units in the randomized list of 70,000 deployed units. This resulted in sporadicconcentrations of production months, but the overall sample still spans the time period over

which CSE produced SR-100s under the prevailing construction method. Similar to phase 1,

collected units were inspected according to the manufacturer criteria. Phase 2 collection and

testing of SR-100s occurred over a period of 3 months.

Test Method

Each recoverable unit was catalogued and photographed. The units were prepared for oxygen

volume evaluation. The start-up oxygen volume was released, measured and compared to themanufacturers established QA criteria. Failure was determined when the volume of start-upoxygen released was less than the age-adjusted minimum volume defined in the CSE quality

assurance plan (Appendix 1). This difference is noted as oxygen volume loss in Table 2.

Results

Age Distribution of Units

Figures 1, 2, and 3 illustrate the manufacturing date frequency among the population at large

(Figure 1), the targeted population (Figure 2), and the tested sample (Figure 3).

A total of 137 SR-100s were collected in phase 1. One hundred and nine units were determined

to be recoverable and subsequently tested, and 28 units were rejected due to one or more failures

during inspection (see Table 1). No units were presented with failing moisture indicators, and

few were presented with unacceptable amounts of physical damage.

During the second phase of collection, units failing the manufacturers inspection criteria were

rejected from inclusion in the oxygen starter study, but the reasons for rejection were no longeranalyzed or tallied. Three hundred ninety-one recoverable units were identified and tested

according to the test plan.

The study was not designed to evaluate the distribution and rate at which field-deployed units

failed to meet the manufacturers standards for continued deployment.

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0 5 10 15 20

Nov-03

Jun-04

Jan-05

Aug-05

Mar-06

Oct-06

May-07

Dec-07

Jul-08

Feb-09

Sep-09

Apr-10

Percent of Units

MonthofManufacture

Population

Figure 1. Age histogram of SR-100 population

Targeted Sample

Feb-04

Aug-04

Feb-05

Aug-05

Feb-06

Aug-06

Feb-07

Aug-07

Feb-08

Aug-08

Feb-09

Aug-09

MonthofManufacture

0 5 10 15 20Percent of Units

Figure 2. Age histogram of targeted sample

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Tested Sample

0 5 10 15 20

Percent of UnitsFigure 3. Age histogram of tested sample

Feb-04

Aug-04

Feb-05

Aug-05

Feb-06

Aug-06

Feb-07

Aug-07

Feb-08Aug-08

Feb-09

Aug-09

MonthofManufactur

e

Table 1. Inspection Failures

Total

Serial No.

28 10

4922

11

0284

11

1535

11

3083

11

6528

11

7030

12

0205

12

4293

13

0302

13

7049

13

7099

13

7613

14

5254

14

6851

16

8662

18

1851

18

7725

18

7902

18

9276

19

1208

20

2636

14

8400

14

8445

20

6317

20

9424

22

3677

23

1516

23

1542

ASMD20

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

HeatIndicator 14 F

ail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Fail

Damage4 F

ail

Fail

Fail

Fail

ASMD = Acoustic Solids Movement Detector

137 units were inspected duringphase 1

All recoverable units were tested according to the procedures outlined in the protocol (Appendix1). NIOSH observed five (5) failures among the 500 units tested (see Table 2).

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Table 2. Start-up oxygen failure details

Test Date

Unit

Serial

Number

Cylinde

r Serial

Number

Manufacture

Date

Volume

of

Oxygen(liters)

QA

MinimumVolume

Oxygen

(liters)

Oxygen

Volume

Deficiency(liters)

Pass/

Fail

Age atTest Date

(Months)

Stored/

Carried(Observation

of current

condition)

02-08-11 154821 A68341 02-2007 3.97 6.4 2.43 Fail 48 Carried

04-19-11 249530A18140

206-2009 5.20 7.4 2.20 Fail 22 Carried

04-19-11 114752 A20125 04-2005 0.02 6 5.98 Fail 72 Carried

04-29-11 251475A18050

3 08-2009 6.09 7.5 1.41 Fail 20 Carried

05-17-11 249607A18131

706-2009 0.93 7.4 6.47 Fail 23 Carried

Overall, the failure discovery rate was 1 per 100 units examined. This rate was observed in both

phases of collection, also suggesting the change in collection methodology did not affect theevaluation. One unit failed among the 109 tested from collection in phase 1, and 4 units failed

among the 391 tested from collection in phase 2.

The 500 tested SR-100s may be viewed as representing three sets of deployed units:(1) SR-100 units deployed at all coal mines using SR-100s (109 collected units, 1 failure

detected),

(2) SR-100 units deployed at coal mines operated by two targeted mining companies (391collected units, 4 failures detected), and

(3) SR-100 units from the combination of sets 1 and 2 (500 collected units, 5 failures detected).

The combined set (3) is considered to be representative of the population of all deployed units.

Recoverable units were photographed prior to being opened for testing. Figures 4 through 9 arephotographs of the units with insufficient start-up oxygen. The photographs illustrate typical

conditions of conforming fielded units. Many other tested units with sufficient start-up oxygen

appeared to have incurred more wear and tear than the average failed unit.

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Figure 4. Unit 154821 Figure 5. Unit 154821 Dented bottom cover.

Figure 6. Unit 249530 Figure 7. Unit 114752

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Figure 9. Unit 251475 Figure 8. Unit 249607

Major Findings

All of the units in which excessive start-up oxygen loss was observed had been carried for atleast some portion of their deployed lives, and exhibited typical conditions of conforming fielded

units. While the unit with the largest total start-up oxygen loss was the oldest of this group, the

next largest total loss measured was in one of the two newest units.

NIOSH observed 5 start-up oxygen failures in the 500 units it tested. By the criteria set forth in

the ASQC sampling tables, the target LQ of 1.25% is not met. The allowable failure rate of 1%

established under the protocol is exceeded.

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Appendix 1

Protocol for Sampling, Testing and Analyzing Oxygen-Starter Performance of the

CSE SR-100 Self-Contained Self-Rescuer

Purpose:

The purpose of this protocol is to establish procedures to sample, test, and analyze the CSE SR-

100 Self-Contained Self-Rescuer (SCSR) oxygen starter performance in mine-deployed

respirators.

Background:

The primary oxygen supply of the CSE, SR-100 SCSR is stored chemically. Upon activation, theSR-100 oxygen starter is designed to provide approximately 9 liters of gaseous oxygen into the

breathing circuit of the SCSR. The injection of gaseous starter oxygen provides initial oxygen

for breathing to allow time for the reaction in the chemical bed to activate and begin producingoxygen for the user. Tests performed as part of the National Institute for Occupational Safety

and Health (NIOSH) Long Term Field Evaluation audit program in December 2009 and by the

manufacturer as part of its quality assurance program, in February 2010, revealed failures ofoxygen starters on some units. CSE has calculated that the oxygen-starter failure rate on new

units is less than one percent. CSE further reported to NIOSH and the Mine Safety and Health

Administration (MSHA) that the oxygen starter failure is related to application of thread sealant

and thread dimensions at the starter oxygen high-pressure valve connection and that the valveconnection assembly process is not traceable to a manufacturing lot or manufacturing date. The

actual oxygen-starter failure rate in field-deployed units is not well characterized at this time.

Based on certification performance requirements established at 42 CFR pt. 84, NIOSH andMSHA have determined that only a fully functioning oxygen starter enables performance of the

SR-100 to be operationally compliant. Starter oxygen is required for proper function in the first

several minutes of use and to ensure a complete oxygen supply. The 42 CFR pt. 84, samplingplans for addressing quality characteristics and the associated manufacturing process accepted

quality levels (AQLs) are found at 42 CFR 84.41:

84.41 Quality control plans; contents.(c) The sampling procedure shall include a list of the characteristics to be tested by the

applicant or his agent.

(d) The characteristics listed in accordance with paragraph (c) of this section shall beclassified according to the potential effect of such defect and grouped into the following

classes:

(1) Critical. A defect that judgment and experience indicate is likely to result in acondition immediately hazardous to life or health for individuals using or depending upon

the respirator;

(2)Major A. A defect, other than critical, that is likely to result in failure to the degreethat the respirator does not provide any respiratory protection, or a defect that reduces

protection and is not detectable by the user;

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(3)Major B. A defect, other than Major A or critical, that is likely to result in reduced

respiratory protection, and is detectable by the user; and(4)Minor. A defect that is not likely to materially reduce the usability of the respirator

for its intended purpose, or a defect that is a departure from established standards and has

little bearing on the effective use or operation of the respirator.

(e) The quality control inspection test method to be used by the applicant or his agent foreach characteristic required to be tested shall be described in detail.

(f) Each item manufactured shall be 100 percent inspected for defects in all criticalcharacteristics and all defective items shall be rejected.

(g) The Acceptable Quality Level (AQL) for each major or minor defect so classified by

the applicant shall be:

(1)Major A. 1.0 percent;(2)Major B. 2.5 percent; and

(3)Minor. 4.0 percent.

According to the NIOSH/MSHA approved quality plan, CSE defines the supply of starter

oxygen for the SR-100 as a critical attribute. The expected failure rate of critical attributes iszero. Test data provided by CSE indicate the actual failure rate to be around one percent.Redundancy in deployment of SCSRs required under 30 CFR 75.1714-4, promulgated under

the Mine Improvement and New Emergency Response Act of 2006, Pub. L. 109-236 (S. 2803),

Section 2 (3)(C)(iii)(II), helps to offset any negative impact from unexpected performanceproblems and in this situation is being relied upon as a temporary solution. In a user notice

offered by CSE on May 10, 2010, CSE acknowledged the benefit of redundancy in the event of

oxygen starter failure, advising that, If for any reason a unit does not inflate the breathing bag,

the user should don another unit if one is readily available. If a second unit is not readilyavailable, the manual start should be used. If an additional SCSR is readily available, the

existing data showing a 1 in 100 (1%) failure rate would yield a 1 in 10,000 chance of havingboth units fail in any sequence of two SCSRs.

As a permanent solution, CSE has proposed redesign of the SR-100, but as of the date of thisprotocol has not submitted plans to NIOSH and MSHA for approval test and evaluation.

However, none of the improvements proposed thus far will address units currently deployed.

Both NIOSH and MSHA expect that currently deployed SR-100s will ultimately need to bereplaced, and that the pace of the replacement needs to be driven by the actual oxygen-starter

failure rate. To that end, a sampling of field-deployed SR-100s is proposed to determine the

prevalence of failed oxygen starters in the CSE SR-100 respirators.

Approach

In order to properly establish the actual prevalence of failed oxygen starters among field-deployed SR-100s, NIOSH proposes using a quality assurance (QA) approach. Operation of the

oxygen starter is a single quality attribute. Defined in this manner, standard QA sampling

methods may be relied upon to yield a statistically significant characterization of the overallnumber of failures by the number of failures observed in a reasonably small sample. The total

mine-deployed population of SR-100s currently exceeds 70,000 units, thus it is crucially

important to draw upon widely recognized sampling techniques and statistical methods. While

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the method proposed is not designed to find the actual proportion of failed starters, it will with

great certainty establish important limits. For example, it will not be possible to state the failurerate is 0.8%, but it will be possible to state the failure rate does not exceed 1.25%, at a 95%

confidence interval. The criteria selected are based around limits of 1.25%, 5%, 8%, and 12.5%.

Criteria

The SR-100 sample selection plan is based on American National Standards (ANSI)/AmericanSociety of Quality (ASQC) Q3-1988, Sampling Procedures and Tables for Inspection of Isolated

Lots by Attributes (Q3-1988). NIOSH regulation 42 CFR 84.43 lists Mil-Std-105D as an

acceptable sampling plan. Mil-STD-105D, as well as the now more widely used ANSI Z1.4,

provides for sampling by Limiting Quality (LQ) levels when the actual consumer risk is at issue.The Q3-1988 is a recognized standard for LQ sampling plans. Q3-1988 plan offers LQ rates for

0.5%, 0.8% and 1.25% nominal limiting quality. It also offers higher LQ rates up to 32%. An

LQ rate of 1.25% represents a 95% confidence level that the lot will have less than 1.25% for thetested characteristic. Thus, a LQ value of 1.25% is a reasonable approximation of a 1%

consumer risk defect level.

To evaluate deployed SR-100 units for sufficient starter oxygen, NIOSH proposes to use Q3-

1988 Limiting Quality (LQ) values. As noted, Q3-1988 lists standard tables of LQ quality levels

ranging from 0.05 to 32 percent for various lot sizes. For a quantity of 35,000 to 100,000deployed SR-100 respirators and LQs ranging from 1.25 to 12.5, the proposed sampling criteria

are:

For LQ 1.25 the sample size is 500 pieces, accept on 3 defects, reject on 4 defects. D=0.27

For LQ 5.0 the sample size is 500 pieces, accept on 18 defects, reject on 19 defects. D=2.5For LQ 8.0 the sample size is 315 pieces, accept on 18 defects, reject on 19 defects. D=3.9

For LQ 12.5 the sample size is 200 pieces, accept on 18 defects, reject on 19 defects. D=6.3Where D = process average percent nonconforming.

Accept means that the lot is determined to be within the LQ, reject means that the lot defect rateexceeds the LQ.

LQ means that there is a 95% probability that the actual lot quality is equal or better than thestated requirement (1.25%). The process average (D), which corresponds to an AQL value, must

be significantly better than the LQ in order to have a 95% probability of acceptance.

With the Q3-1988 plan and a 500-piece SR-100 sample size, information at LQs of 2.0 and 3.15can also be obtained. For LQ 2.0 accept criteria is not more than 5 defects and for LQ 3.15

accept criteria is not more than 10 defects.

Sample Collection

NIOSH will use the current MSHA SCSR inventory of all mine-deployed SR-100 units to

randomize units manufactured after October 2003. The significance of October 2003 relates tosimilarity in design and construction. This is the date when the threads on the SR-100 starter-

oxygen bottle were modified to the current design. The heat-exposure indicator was also added

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to the SR-100 in that timeframe. (Fewer than 4700 of the currently deployed SR-100s in service

in mines are older than this cut-off.)

Using the MSHA inventory, and the unit serial number as a unique identifier, all in-service SR-

100s newer than October 2003, will be randomized. As defined in Q3-1988, a sample size of

500 is needed to ascertain the target LQ values at the stated level of confidence (95%). Pastexperience collecting SCSRs from mine service indicates that more than 500 units will need to

be assessed in order to obtain 500 recoverable units for testing. A recoverable unit is a unit thatcan be found and passes all manufacturer inspection criteria for use. There are numerous reasons

that individual units may not be found. Foremost among the reasons is that a unit reported in the

inventory can be damaged and removed from service between the time it is recorded and the time

that it is searched for in the collection. NIOSH will tabulate and organize the randomly selectedunit serial numbers by MSHA District and request each District to retrieve the SR-100s on its

respective list. All units not recoverable shall be noted as such on the sample inventory list

provided to the Districts, and the reason for which they are deemed to be unrecoverable shallalso be made part of that record. NIOSH will then retrieve units from the MSHA Districts.

The ultimate goal of the collection is to assemble the lowest-ordered-500 randomly-listed,recoverable units available for testing. Since the logistics of sample collection and retrieval are

not trivial, NIOSH proposes to accumulate these from the MSHA Districts in at least two forays

to reduce the amount of over-selection needed to obtain the required sample. Units retrieved byNIOSH from the MSHA district offices will be re-inspected in the NPPTL lab by a NIOSH

technician and tested in an order that ensures the goal of the collection, mentioned above, is met

in full.

NIOSH also wishes to reserve the ability to evaluate the test results in the most efficient manner

permitted under the QA sampling plan. For instance, if 19 defects were to be observed withinthe first 100 units tested, the sample collection, if it has not already been completed, and testing

could be halted. In that event, the logic of the QA sample plan indicates the highest selected lot

rejection criterion has been exceeded at the number of observations. We would not know whatthe actual prevalence is, but we would know that the QA percent defective exceeds 12.5%, and a

replacement rate decision could be made on that basis. Appendix A details some critical

sampling plan decision points based on the number of defects observed.

Test Plan Outline

1. Record the SR-100 unit serial number and date of manufacture.2. Determine the minimum allowable volume of starter oxygen based on unit date of

manufacturer and CSE maximum allowable leakage rate.

3. Open SR-100a. If unable to open put the unit aside and do not use for this evaluation.b. If the unit opens proceed to step 4.

4. Record serial number of oxygen starter cylinder.5. Measure volume of starter oxygen available. The breathing bag will be removed

from the unit and the unit connected to a spirometer and an electronic data

recorder for the volume measurement.

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6. Compare measured volume of starter oxygen available with the minimum

allowable oxygen volume from step 2.7. Test result:

a. If the volume of starter oxygen available is equal to or greater than () theminimum allowable starter oxygen the unit is an accept (PASS);

b.

If the volume of starter oxygen available is less than (


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Attachment 1

Condition Measured Defect

Rate, R

Effective Failure Rate

w/redundancy

A R 12.5% at least 1 in 100

*A measured defect rate of 3% represents the approximate point at which the effective failure

rate in any sequential selection of two units rises above 1 in 1000.

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DHHS (NIOSH) Publication No. 2012-139

SAFER HEALTHIER PEOPLE
mailto:[email protected]://www.cdc.gov/nioshhttp://www.cdc.gov/niosh/eNewsmailto:[email protected]://www.cdc.gov/nioshhttp://www.cdc.gov/niosh/eNews

DHHS (NIOSH) Publication No. 2012-139, Loss of Start-Up Oxygen in CSE SR-100 Self-Contained Self-Rescuers 2012-139[1]

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